Need another reason to get a good night’s rest? In one recent study, when people were sleep restricted, they lost 55% less body fat than those who got a full night’s rest – even if total weight loss was the same. And they felt hungrier in the process. Those with adequate rest produced less of the hormone ghrelin that stimulates appetite and reduces energy expenditure. So if your goal is to lose body fat, then a full night’s sleep is an important part of your diet plan.

In a study published in the journal Annals of Internal Medicine, 10 overweight but healthy volunteers aged 35-49 were placed on a diet targeted to provide 90% of what each person needed to maintain his or her weight without exercise. The average calories consumed were 1,450 calories per day. Subjects were studied twice under identical conditions in a laboratory, except for the amount of sleep time allowed.

All participants spent the first 14 days in the lab with 8.5 hours allowed for sleep time. Following the first phase, study subjects underwent 14 additional days in the lab with only 5.5 hours of sleep permitted. The actual sleep hours averaged about 7.5 hours in the first phase and 5.25 hours in the second phase, more than two precious sleep hours less. Non-sleep time was spent engaged in home or office-like work or leisure activities.

Due to the calorie restriction, volunteers lost an average of 6.6 pounds during each of the 14-day sessions. However, during the adequate sleep phase, subjects loss 3.1 pounds of fat of the 6.6-pound total loss. But during the restricted sleep phase, participants lost only 1.3 pounds of fat. The rest of their weight loss was of fat-free body mass, mostly protein.

Restricted sleep also correlated with more hunger and higher levels of ghrelin, which rose by an average of 12% compared to adequate sleep levels. Gherlin is known to stimulate hunger and food intake, reduce calories burned by the body, promote retention of fat, and increase the amount of glucose produced by the liver – all of which make successful dieting and fat loss more difficult.

Ghrelin is produced in the stomach. The level rises before a meal and decreases afterward. The hormone not only stimulates the brain, but also favors the accumulation of blood lipids in the fat around your internal organs – so called visceral fat.

The accumulation of visceral fat correlates with higher blood pressure, type 2 diabetes and liver fat. As visceral fat accumulates, the body becomes less sensitive to insulin and the cells may develop insulin resistance. The combination of high blood pressure, elevated blood lipids and insulin resistance may lead to metabolic syndrome and a variety of cardiovascular and endocrine abnormalities.

Of note, a recent animal study conducted by researchers at Yale University found that gherlin triggers the same nerve cells that are activated by delicious food, sexual experience and many recreation drugs. These are the neurons that provide the sensation of pleasure and the expectation of reward. No wonder dieting can be so difficult!